What is bacterial (or infective) endocarditis?
Bacterial (or infective) endocarditis is a rare condition in which one of the heart valves becomes infected. In most cases only valves that are already abnormal are affected, and those with congenital heart abnormalities can be at risk. Bacterial endocarditis is a serious disorder, which was fatal before the use of antibiotics became widespread. Now most cases
recover well although surgery may be necessary if the valve damage is severe.
Bacterial endocarditis is an infection of the inner surface of the heart or the heart valves caused by bacteria usually found in the mouth, intestinal tract or urinary tract. This infection results in a serious illness which requires prolonged treatment and on occasion produces injury to the heart or even death. Endocarditis is a major concern in almost all unrepaired congenital heart defects as well as in most repaired defects with a few exceptions. Endocarditis is generally preventable with simple measures, but the implementation of these measures is often confusing for the parents of thechild, the physician, and the dentist. Hopefully this brief article will decrease some of that confusion.
Endocarditis can be classified as either infective or non-infective, depending on whether a foreign organism is causing the problem. As the valves of the heart do not actually receive any blood supply of their own, which may be surprising given their location, defense mechanisms (such as white blood cells) cannot enter. So if an organism (such as bacteria) establish hold on the valves, the body cannot get rid of them.
Normally, blood flows pretty smoothly through these valves. If they have been damaged (for instance in rheumatic fever) bacteria have a chance to take hold. Traditionally, infective endocarditis has been divided into acute and sub-acute endocarditis. This terminology is now discouraged, as the word sub-acute is considered an oxymoron. Nowadays, the terms short incubation (meaning about less than six weeks), and long incubation (greater than six weeks), are preferred.
Infective endocarditis may also be classified as culture-positive or culture-negative. Culture-negative endocarditis is due to micro-organisms that require a longer period of time to be identified in the laboratory. Such organisms are said to be fastidious because they have demanding growth requirements. Some pathogens responsible for culture-negative endocarditis include Aspergillus species, Brucella species, Coxiella burnettii, Chlamydia species, and HACEK bacteria. Finally, the distinction between native-valve endocarditis and prosthetic-valve endocarditis is clinically important.
As previously mentioned, altered blood flow around the valves is a risk factor in obtaining endocarditis. The valves may being damaged congenitally, from surgery, by auto-immune mechanisms, or simply as a consequence of old age. The damaged part of a heart valve becomes covered with a blood clot, a condition known as non-bacterial thrombotic endocarditis (NBTE). In a healthy individual, a bacteraemia, (where bacteria get into the blood stream through a minor cut or wound,) would normally be cleared quickly with no adverse consequences. If a heart valve is damaged and covered with a piece of blood clot, this provides a place for the bacteria to attach themselves, and an infection is established.
The bacteraemia is often caused by minor dental procedures, such as a tooth removal. It is important that a dentist is told of any heart problems before commencing. Another group of causes result from a high number of bacteria getting into the bloodstream. Colorectal cancer, serious urinary tract infections and IV drug use, can all introduce large numbers of bacteria. With a large number of bacteria, even a normal heart valve may be infected. A more virulent organism (such as Staphylococcus aureus) is usually responsible for infecting a normal valve.
Intravenous drug users tend to get their right heart valves infected because the veins that are injected enter the right side of the heart. The injured valve is most commonly affected when there is a pre-existing disease. (In rheumatic heart disease this is the aortic and the mitral valves, on the left side of the heart.)